An original should be a stone litho
You can look at how it is printed (with a jewlers loop or a magnifiying glass).
Tiny dots will be the giveaway (printing press).
If not dot's, it still may not be real, but there's a much better chance it is.
The character of the paper is also a concern.
Is it very thin. If not linen mounted, looking at the back will show the age and color lines.
Also, on the back there should be some purple or black hand stamp marks along a fold line.
However any of this, can be faked. Vintage paper is avail, and stamps can be stamped.